Authorities in Texas said on Monday that they have thwarted a "mass casualty attack" after arresting a suspect who allegedly made terroristic threats against police officers.

       The suspect, Seth "Andrea" Gregori, allegedly expressed "clear planning, intent and steps taken to ambush and kill police officers in Corpus Christi, Texas," according to court records obtained by ABC News.

       Gregori was arrested on a terroristic threats warrant Monday morning, the Corpus Christi Police Department said.

       "The Federal Bureau of Investigation was notified of Gregori making terroristic threats against Corpus Christi Police Department Officers," the police department said in a statement. "The Federal Bureau of Investigation investigated the threats and secured an arrest warrant for Gregori."

       The investigation began on Feb. 6, after a friend of Gregori's told police the suspect reported being in possession of an AR-15 pistol and had expressed a desire to kill Corpus Christi officers, according to an arrest warrant obtained by ABC News.

       That friend, whose name was redacted, sent police text messages that showed "a lengthy history of the offender wishing to carry out a 'Dallas style' attack on police," the warrant affidavit stated.

       The 21-year-old suspect allegedly planned an attack on police "similar to the 2016 Dallas ambush," the FBI's Houston office said.

       In the 2016 incident referenced by the FBI, five Dallas police officers were killed and nine injured in an ambush-style shooting.

       The shooter, Micah Xavier Johnson, told a hostage negotiator that he wanted to kill white people, especially police officers, and expressed anger for Black Lives Matter, police said. The ex-U.S. Army reservist was killed by police when they detonated a bomb delivered by a robot.

       Gregori allegedly mentioned Johnson by name in the text messages, according to the affidavit.

       "Yes, I've planned on shooting and killing cops as much as I could like Micah planned it for years," Gregori allegedly said in a message to the friend, according to the affidavit.

       "Andrea/Seth then sent a picture of the side of an AR receiver," the document continued.

       The friend told police there were "thousands of messages" sent by the suspect, but police asked for them to be pared down to the "worst" and "most recent" messages, according to the affidavit.

       Police received 71 pages as evidence.

       Some text messages included 19 images from the Dallas crime scene and of Johnson, according to the affidavit. There were three images "taken surreptitiously stalking local police officers along with messages of how the offender reenacted the Dallas shooting with the officers in the images unaware," it said.

       Gregori allegedly said the plan would be carried out "downtown like Micah because it looks like Dallas," the affidavit stated.

       "He states he will avoid innocent bystanders because he is a sharpshooter, only targeting cops and goes onto clarify several times throughout the messages that he only wants to target CCPD (Corpus Christi Police Department)," the affidavit stated. "The offender states he further only wishes to target 'white' cops leaving the 'black and Mexican cops alone.'"

       No charges have been filed yet in the case, the Nueces County District Attorney's Office told ABC Corpus Christi affiliate KIII on Monday.

       It is unclear if Gregori has an attorney at this time.