SAN ANTONIO, TX --The man accused of the late-night, ambush-style slaying of a South Texas sheriff's sergeant as the officer's cruiser waited at a red light in San Antonio was drunk and on anti-depression medication but has no apparent links to drug smugglers or streets gangs, investigators said Monday. Mark Anthony Gonzales, 41, was arrested on suspicion of capital murder after SWAT teams from the FBI and the Bexar County Sheriff's Office swarmed a double-wide mobile home about 15 miles south of San Antonio on Sunday, Sheriff Amadeo Ortiz said at a news conference. The raid came after one of the suspect's friends told police that Gonzales was likely behind the shooting of Sgt. Kenneth Vann, Ortiz said. Vann died in a hail of gunfire from an automatic weapon in the early hours of May 28. Ortiz said authorities recovered from the trailer an MP-15 rifle and other guns that fire .223-caliber rounds, along with an ammunition magazine that they believe was used in Vann's killing. The FBI is analyzing a blue pickup registered to Gonzales, which was recovered at a local body shop. Gonzales refused to answer questions from investigators, Ortiz said. His wife, who was home at the time of the raid, was briefly interrogated and released. Gonzales did not yet have an attorney Monday, sheriff's officials said. The motive for the killing remains a mystery because the shooter probably knew from the markings on the car that he was targeting a police officer, but he likely didn't know the identity of the officer inside, Ortiz said. "There is no indication that the drug cartels were involved. There's no indication this was a gang initiation," Ortiz said. "This individual seemed to be a loner and didn't really associate with too many people." Ortiz said a friend who had been with Gonzales the day of the shooting suspected he could have been involved but was afraid to contact authorities. When the friend eventually told his wife, however, she called U.S. marshals -- a tip that led to the arrest. "He didn't want to call. He was afraid. He was afraid for his friend," Ortiz said. "But finally, he confided in his wife." Gonzales spent much of the day of the shooting drinking beer and wine and had been taking medication for depression, Ortiz said. The sheriff also said Gonzales once applied to become a San Antonio police officer but never completed the process. Vann was responding to a call and waiting at a light near a San Antonio freeway when a vehicle, believed to be Gonzales' blue pickup truck, pulled up behind his patrol car and fired dozens of shots around 2 a.m., Ortiz said. Authorities don't believe Vann was specifically targeted because surveillance video showed no indication that he was being followed. Ortiz said sheriff's deputies usually cruise outside San Antonio, so it's possible the shooter thought he was targeting a city police officer. A reward of $127,000 had been offered from donations by the FBI, individuals, police agencies and associations, and Vann's family. Ortiz said the money would be shared among at least two people. Vann was buried with full military and sheriff's office honors last week. His widow, fellow sheriff's Sgt. Yvonne Vann, told reporters Monday that she thinks Gonzales probably didn't know what he was doing and "that he was signing his own death warrant." A capital murder charge could carry the death penalty. "Drunk and medication obviously don't combine," Yvonne Vann said. "I'm not using that as an excuse for the motive and what he did, but who knows what he was thinking at that time." Yvonne Vann said she has not been allowed to speak to Gonzales since he has been in custody. But if she were given the opportunity, she said she would tell him: "There's no excuse for what you did. You're going to have `man up' and face the consequences."