Odessa Police Chief Michael Gerke said the suspect, 36-year-old Seth Aaron Ator, was fired from his job at the Journey Oil Services on Saturday morning, AP reported, hours before the mass shooting that left seven dead and at least 22 others injured.

After his termination, Ator made “rambling” phone calls to the FBI national tip line and 911, according to authorities.

Gerke, during a press conference on Monday, revealed that the company also called 911, but Ator had fled the scene by the time authorities arrived at the office premises. “Basically, they were complaining on each other because they had a disagreement over the firing,” Gerke said.

FBI Special Agent Christopher Combs said Ator arrived at work “in trouble” that day.

A Texas state trooper pulled the suspect over roughly 15 minutes later, at around 3:15 p.m. local time, between Odessa and Midland for failing to signal a lane change. Police say Ator opened fire on the trooper, before turning to shoot at random vehicles and passersby.

The suspect then headed West towards Odessa while shooting at other victims. The gunman later deserted his vehicle and hijacked a U.S. Postal Service van. He was later killed during a shootout with authorities near a Cinergy movie theatre.

“The reason that person was stopped was because of a Midland police officer and an Odessa police officer. They rammed his car, stopped him and when he got out, they shot him,” Odessa Mayor David Turner said.

During the Monday press conference, a representative for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said that Ator had attempted to obtain a gun before the shooting but did not pass a background check. Authorities are “aggressively following up on” the source that gave Ator the firearm, according to CNN.

Ator is believed to have acted alone but authorities have not yet established a motive for the shooting.

A 17-month-girl, Anderson Davis, and three law enforcement officers were among those injured in the incident on Saturday. Davis reportedly suffered shrapnel impact to her right chest as well as a gunshot wound through her bottom lip, according to NBC News. Davis is being treated at a Lubbock hospital and is in satisfactory condition, said Eric Finley, marketing director of Texas’ UMC Health System.

“We praise God for walking beside us during this time and our prayers go out to all of the families that are walking this same walk,” Anderson’s parents said in response to the incident. “We hurt so badly for the families whose loved ones didn’t survive this tragedy.”