执法人员正在调查对唐纳德·特朗普的暗杀企图据几位执法官员和了解此事的议员说，他周三告诉议员，从美国特勤局狙击手在屋顶上首次发现枪手到向前总统开枪的时间过去了20分钟。

　　官员们表示，狙击手在美国东部时间下午5点52分，在宾夕法尼亚州巴特勒的集会上，在安全区外的一座建筑的屋顶上发现了20岁的嫌疑人托马斯·马修·克鲁克斯。消息人士称，枪击发生在美国东部时间下午6点12分，20分钟后。

　　在枪击事件发生后的几天里，特勤局因其对暗杀企图的反应受到审查，该局局长金伯利·谢特尔(Kimberly Cheatle)被传唤到国会作证。国土安全部发言人表示，她“欢迎作证的机会。”

　　消息人士告诉美国广播公司新闻，克鲁克斯在他的手机上搜索了乔·拜登总统和前总统特朗普的图像，并搜索了特朗普在巴特勒集会的日期和芝加哥民主党全国代表大会的日期。

　　电话搜索记录显示没有迹象表明克鲁克斯的政治观点，调查人员正试图确定他的动机。

　　据执法官员和议员介绍，美国联邦调查局局长、副局长和特勤局局长告诉议员，在枪击事件发生整整62分钟前，克鲁克斯被确定为嫌疑人。

　　根据消息来源，简报中提出的时间表如下:

　　下午5点10分，克鲁克斯第一次被认定为嫌疑人

　　下午5:30有人用测距仪发现了克鲁克斯

　　下午5:52特勤局发现克鲁克斯在屋顶上

　　下午6点02分，特朗普上台

　　下午6点12分，克鲁克斯开了第一枪

　　据执法官员称，从克鲁克斯开第一枪到枪手被击毙仅用了26秒。第一声枪响后11秒，特勤局反狙击手锁定了目标——15秒后，克鲁克斯被击毙。

　　简报者告诉立法者，7月5日，在集会宣布两天后，克鲁克斯在沃尔玛购买了一个弹药箱。7月13日，他早上去了集会地点，在那里呆了一个小时后离开。他在下午5点左右回来，并试图在下午5:30左右进入安全区。

　　美国广播公司新闻的视觉验证小组的新分析显示，在第一声枪响之前，驻扎在集会舞台后面南北两侧建筑物顶上的两个狙击小组中的一个。下午6点09分，在第一声枪响前两分钟，舞台以南距离枪手位置最远的大楼屋顶上的狙击小组重新定位，从枪手所在位置的方向由南向北转向。

　　根据通报者的说法，暗杀企图的动机仍然是一个谜，他们没有发现特朗普和/或拜登有任何意识形态上的联系。

　　根据对枪手父母的采访，执法部门告诉成员们，他们认为两人都没有强烈的政治倾向。

　　一位消息人士称，美国联邦调查局告诉立法者，作为调查的一部分，他们已经进行了200次采访。

　　时间线成为焦点

　　知情人士告诉美国广播公司新闻，克鲁克斯爬上一栋建筑的空调设备，爬到相邻建筑的顶部开枪，从而能够清楚地击中前总统。

　　根据执法部门的消息，在实施无耻的暗杀企图前几分钟，有人看到他在磁强计附近走来走去，在那里拉力赛选手在进入室外场地前被扫描武器。

　　新的旁观者视频由匹兹堡ABC子公司WTAE独家获得的照片显示，周六下午5点06分，克鲁克斯在特朗普集会的边界外踱步-大约在第一次开枪前1小时5分钟。执法人员称，他们认为这段视频显示的是骗子。

　　多个消息来源告诉美国广播公司新闻，在枪击发生前几分钟，克鲁克斯出现在金属探测器区域，引起了执法人员的注意，他们开始怀疑并开始接近他。据消息人士称，当时，这名潜在的刺客后退，消失在人群中。不清楚枪击发生前多久。

　　消息人士称，在他被发现靠近磁力计的时间和克鲁克斯据称向特朗普开枪的时间之间，有两组无线电传输，一组报告警方正在寻找一个可疑的人，另一组更通用的警告是警察正在跟踪可疑的东西。

　　消息人士称，当警察开始搜寻可疑人员时，克鲁克斯来到了美国玻璃研究中心(AGR)大楼的区域，该区域位于为该活动设立的安全警戒线之外。特勤局局长Cheatle在本周的一次独家采访中告诉ABC新闻，当时，这座建筑被用作当地警察的集结地，他们就在建筑内。

　　更具体地说，消息人士告诉美国广播公司新闻，AGR大楼里有当地警察和反狙击手部队，克鲁克斯最终在那里占据了向特朗普开火的位置。据消息人士称，调查人员认为，这可能导致混乱，因为特勤局狙击手试图确定特朗普是否面临威胁，以及威胁可能来自哪里。

　　消息人士称，部署在集会舞台附近建筑上的特勤局反狙击手知道AGR大楼被执法部门用作集结地。消息人士称，调查人员认为这可能导致特勤局神枪手的反应延迟，因为他们必须首先弄清楚嫌疑人是否是一个威胁。

　　但消息人士称，一旦有人向前总统开枪，特勤局的狙击手就再也等不及了，将枪手击毙。

　　“找出那个人，找到他们，识别他们，并最终消除他们是在很短的时间内发生的，这使得它非常困难，”Cheatle在接受美国广播公司新闻采访时说。

　　与此同时，两名熟悉情况的消息人士周三告诉美国广播公司新闻，在集会之前，特勤局要求当地警方在AGR大楼部署巡逻车，但当地警方官员无法提供。《华盛顿邮报》首先报道了这一细节。

　　尽管执法部门消息来源称骗子据信他在枪击前在家得宝购买了一把5英尺长的梯子，它似乎没有被用来爬上屋顶，也没有在现场被发现。

　　消息人士称，调查人员认为，克鲁克斯爬上从地面可以接触到的邻近建筑的空调设备，爬上屋顶，来到开枪的地点。据执法部门消息人士称，从那里，他设法进入了邻近大楼的顶部，目击者告诉美国广播公司新闻，他们看到他爬上屋顶的斜坡，来到他向特朗普开了八枪的地方，特朗普正在大约400英尺远的讲台上讲话。

　　作为联邦调查局调查周三继续，关于枪手如何能够不受阻碍地爬上屋顶，获得一个直接视线并对前总统连珠炮似的扫射。

　　消息人士说，当克鲁克斯走向他的射击位置时，特勤局特工正在收听警方正在寻找的可疑人员的无线电通信，并听到当地执法部门谈论涉及警察的某种对抗。

　　巴特勒县警长迈克尔·t·斯卢普(Michael T. Slupe)告诉美国广播公司新闻，他从其他执法官员那里得知，一名正在搜索可疑人员的巴特勒镇警察跳上了AGR大楼的屋顶，并与枪手短暂对峙，枪手将武器转向这名警察，导致他向后撤退。几分钟后枪声响起。

　　可疑设备

　　据执法部门消息人士称，调查人员周二表示，他们在嫌疑人的口袋中发现了一个远程发射器，该发射器可能旨在引发嫌疑人汽车中发现的两个可疑装置和他家中的一个装置。消息人士称，这两个地点的装置都是在弹药容器中类似地构建的，使用的组件包括接收器，这些接收器似乎与嫌疑人口袋中找到的遥控器配对。

　　每个装置中的接收器都连接到一系列部件上，调查人员称这些部件符合“眼睛测试”的要求，这些部件可以制造出可行的爆炸物，尽管这些装置的功能仍有待确定。这些装置的用途也不清楚。目前还不清楚这些炸弹是有意制造大爆炸来伤害人们，还是旨在制造烟雾、火灾和低强度爆炸来转移注意力。

　　调查人员还在嫌疑人的汽车中发现了一件战术背心，尽管尚不清楚他为什么没有在袭击前总统集会时穿着它。一些调查人员怀疑他是否预料到会死于袭击。

　　根据执法部门的消息，枪手还问他的雇主周六是否可以休息一天，但他说他可能最早在周日，也就是袭击发生后的第二天就可以回去工作。但到目前为止，调查人员没有发现任何迹象表明他有任何同伙或其他支持来实现他的致命目标。

　　过去被欺负

　　美国联邦调查局现在已经解锁了他的手机，对他的手机的检查没有发现任何关于嫌疑人动机的重要信息——只有消息来源描述为一个20岁男性的“例行”信息。

　　调查人员发现，迄今为止，克鲁克斯是一个没有朋友的孤独者。根据调查的初步结果，了解调查的多个消息来源告诉ABC新闻，他是“奇怪的”。消息人士称，美国联邦调查局分析师正试图评估克鲁克斯是难以接近还是因为他在隐藏什么而被关闭。

　　一位消息人士称，克鲁克斯过去曾被“欺负”过一点，但针对他的行为“并不过分”。

　　调查人员正在积极寻找，看看是否有骗子通过使用“燃烧器”或其他通信设备来掩盖他的踪迹。

　　宾夕法尼亚州警方在一份声明中表示，它向特勤局提供了“所有资源”,包括30至40名警察，以协助确保竞选集会场地的内部安全，但“不负责保护安全周界以外的建筑或财产”,在那里，潜在的刺客开火了。

　　在一个美国广播公司新闻的独家采访Cheatle证实，在枪手在屋顶向特朗普开枪的同时，当地警察也在大楼内。Cheatle还说，当地政府的任务是确保该建筑的安全。

　　“在这种特殊的情况下，我们确实分享了对特定地点的支持，特勤局负责内部周界，”Cheatle说。"然后我们向当地的同行寻求外围的帮助."

　　Secret Service spotted Trump rally shooter on roof 20 minutes before gunfire erupted

　　Law enforcement officials investigating theassassination attempt on Donald Trumptold lawmakers Wednesday that 20 minutes passed between the time U.S. Secret Service snipers first spotted the gunman on a rooftop and the time shots were fired at the former president, according to several law enforcement officials and lawmakers briefed on the matter.

　　Officials said the snipers spotted the suspect, 20-year-old Thomas Matthew Crooks, on the roof of a building outside the security zone at the rally in Butler, Pennsylvania, at 5:52 p.m. ET. The shooting happened at 6:12 p.m. ET, 20 minutes later, the sources said.

　　In the days since the shooting, the Secret Service has come under scrutiny for its response to the assassination attempt and the agency's director, Kimberly Cheatle, has been subpoenaed to testify before Congress. A Department of Homeland Security spokesperson said she "welcomes the opportunity to testify."

　　The revelation of the timeline came as sources told ABC News that Crooks searched on his phone for images of President Joe Biden and former President Trump and searched for the dates of Trump’s rally in Butler and for dates of the Democratic National Convention in Chicago.

　　The phone search history revealed no indication of Crooks’ political views and investigators were trying to determine his motive.

　　The FBI director, his deputy director and the head of the Secret Service told lawmakers Crooks was identified as a person of interest a full 62 minutes before the shooting took place, according to the law enforcement officials and lawmakers briefed.

　　According to the sources, the timeline presented in the briefing was as follows:

　　5:10 p.m. Crooks was first identified as a person of interest

　　5:30 p.m. Crooks was spotted with a rangefinder

　　5:52 p.m. Crooks was spotted on the roof by Secret Service

　　6:02 p.m. Trump takes the stage

　　6:12 p.m. Crooks fires first shots

　　From the time Crooks fired his first shot to the gunman being killed was just 26 seconds, according to law enforcement officials. Eleven seconds after the first shot, Secret Service counter snipers acquired their target -- and 15 seconds after that, Crooks was shot dead.

　　Briefers told lawmakers that Crooks purchased an ammunition box at a Walmart on July 5, two days after the rally was announced. On July 13, he went to the rally site in the morning, was there for an hour and then left. He came back sometime in the early 5 p.m. hour and tried to enter the security perimeter at around 5:30 p.m.

　　New analysis by ABC News' visual verification team reveals that one of two sniper teams posted atop buildings to the north and south behind the rally stage repositioned before the first gunshots were fired. At 6:09 p.m., two minutes before the first gunshots rang out, the sniper team on the roof of the building south of the stage, the furthest away from the shooter’s location, repositioned, turning from the south to the north in the direction of the shooter’s location.

　　The motive for the assassination attempt remains a mystery, according to the briefers, and they have not identified any ideological nexus to Trump and/or Biden.

　　Based on interviews with the shooter's parents, law enforcement told members they believe that neither has strong political leanings.

　　The FBI told lawmakers they've conducted 200 interviews as part of the investigation, a source said.

　　Timeline comes into focus

　　Minutes before pulling off the brazen assassination attempt, he was seen walking around near the magnetometers where rallygoers were being scanned for weapons before entering the outdoor venue, according to law enforcement sources.

　　Newbystander videoobtained exclusively by Pittsburgh ABC affiliate WTAE appears to show Crooks pacing just beyond the boundaries of the Trump rally at 5:06 p.m. Saturday -- about 1 hour and 5 minutes before shots were first fired. Law enforcement sources said they believe this video shows Crooks.

　　Crooks' presence in the area of the metal detectors in the minutes before the shooting caught the eye of someone in law enforcement who became suspicious and started to approach him, multiple sources told ABC News. At that point, the would-be assassin backed up and faded into the crowd, according to sources. It was not clear how long before the shooting this happened.

　　Between the time he was spotted near the magnetometers and when Crooks allegedly fired at Trump, there were two sets of radio transmissions, one reporting that police were looking for a suspicious person and another more generic warning that officers were following up on something suspicious, sources said.

　　As officers began searching for the suspicious person, Crooks made his way to the area of the American Glass Research (AGR) building outside the security perimeter established for the event, the sources said. At the time, the building was being used as a staging area for local police, who were inside the structure, the Secret Service director, Cheatle, told ABC News in an exclusive interview this week.

　　More specifically, sources told ABC News that there were local police personnel and counter-sniper units in the AGR building where Crooks eventually took up a position to fire at Trump, sources said. Investigators believe that could have led to confusion as Secret Service snipers were trying to determine whether there was a threat to Trump and where it might be coming from, according to the sources.

　　Secret Service counter snipers positioned on buildings close to the rally stage were aware the AGR building was being used as a staging area by law enforcement, sources said. Investigators believe that could have led to a delay in the Secret Service sharpshooters' reactions because they had to first figure out whether the suspect was a threat, sources said.

　　But once shots were fired at the former president, the Secret Service snipers could not wait any longer and took out the gunman, sources said.

　　"Seeking that person out, finding them, identifying them, and eventually neutralizing them took place in a very short period of time, and it makes it very difficult," Cheatle said during the interview with ABC News.

　　Meanwhile, two sources familiar with the situation told ABC News Wednesday that before the rally, the Secret Service requested a local police cruiser to be positioned at the AGR building, but local police officials were not able to provide one. The detail was first reported by the Washington Post.

　　Though law enforcement sources saidCrooksis believed to have purchased a 5-foot ladder at a Home Depot before the shooting, it does not appear to have been used to climb on the roof and was not found at the scene.

　　Investigators believe Crooks made his way to the spot where he fired from by scaling an air conditioning unit of an adjacent building accessible from the ground and pulling himself up onto the roof, sources said. From there, he managed to gain access to the top of the neighboring building, where witnesses told ABC News they saw him shimmying up the slope of the roof to the area where he got off up to eight shots at Trump who was speaking at a podium about 400 feet away, according to law enforcement sources.

　　As theFBI investigationcontinued Wednesday, questions swirled about how the gunman was able to ascend unimpeded to the roof, gain adirect line of sightand fire a barrage of shot at the former president.

　　While Crooks was making his way to his shooting position, Secret Service agents were listening to radio traffic about a suspicious person police were looking for and heard local law enforcement talking about some sort of confrontation involving police, the sources said.

　　Butler County Sheriff Michael T. Slupe told ABC News that he was informed by other law enforcement officials that a Butler Township police officer searching for the suspicious person was vaulted onto the AGR building's roof and briefly confronted the gunman, who turned his weapon to the officer, causing him to retreat back down. Shots rang out moments later.

　　Suspicious devices

　　Investigators said Tuesday they found a remote transmitter in the suspect's pocket that may have been intended to set off two suspicious devices found in the suspect's car and one in his home, according to law enforcement sources. Devices at both locations were similarly constructed in ammunition containers using components including receivers that appear to have been paired with the remote control found in the suspect's pocket, sources said.

　　The receivers in each device were connected to a series of components that investigators say met the "eye test" -- having parts present that could have made viable explosives, although the functionality of the devices is still being determined. The purpose of the devices is also unknown. Whether they were intended to cause a significant blast to hurt people or if they were designed to create smoke, fire and a low-grade blast for a diversion is unclear.

　　Investigators also found a tactical vest in the suspect's car, though it is unclear why he did not wear it during the assault on the former president's rally. Some investigators are wondering whether he anticipated dying in the attack.

　　The shooter also asked his employer if he could take a day off on Saturday but said he would return to work perhaps as soon as Sunday, the day after this attack, according to law enforcement sources. But thus far, investigators have turned up nothing to suggest that he had any accomplices or other support to carry out his deadly objective.

　　'Bullied' in the past

　　An examination of his phone, which the FBI has now unlocked, has not turned up any significant information about the suspect's motives -- only what sources described as "routine" information for a 20-year-old male.

　　Investigators have found, so far, that Crooks was a loner without friends. He was “odd,” according to preliminary findings in the probe, multiple sources briefed on the investigation told ABC News. FBI analysts are trying to assess whether Crooks was hard to get close to or was shut off because he was hiding something, sources said.

　　Crooks had been “bullied” a little in the past, but the acts against him were “not over the top,” one source said.

　　Investigators are actively looking to see if perhaps Crooks covered his tracks by using “burners” or other communication devices.

　　The Pennsylvania State Police said in a statement that it provided "all resources" to the Secret Service -- including 30 to 40 troopers to assist with securing the inside perimeter of the campaign rally venue -- but "was not responsible for securing the building or property" outside the security perimeter where the would-be assassin opened fire.

　　In anexclusive interview with ABC News, Cheatle, confirmed that local police were present inside the building at the same time the shooter was on the roof firing at Trump. Cheatle also said that local authorities were tasked with securing that building.

　　"In this particular instance, we did share support for that particular site and that the Secret Service was responsible for the inner perimeter," Cheatle said. "And then we sought assistance from our local counterparts for the outer perimeter."