OAKLAND, CA — Former NFL running back Doug Martin was battling through mental health issues before his death Saturday while in the custody of the Oakland Police Department, his former agent said on behalf of the footballer’s family.

It’s still unclear what caused the 36-year-old’s death. His parents were trying to get him medical assistance on Saturday and had called authorities for support, according to a statement by Brian Murphy, Martin’s former agent.

But Martin, feeling overwhelmed and disoriented, left his Oakland home, according to the statement. He then entered a neighbor’s home two doors down, his family said.

Police were called to the neighbor’s home in the 11000 block of Ettrick Street around 4:15 a.m. There, they tried to detain Martin, and after a brief struggle, were able to take him into custody, the Oakland Police Department said Monday.

Martin became unresponsive soon after, and he was taken to a local hospital where he died, police said.

“Privately, Doug battled mental health challenges that profoundly impacted his personal and professional life,” Murphy said. “Ultimately, mental illness proved to be the one opponent from which Doug could not run.”

An investigation into Martin’s death is underway, and the officers involved have been placed on paid administrative leave, as is the Oakland Police Department’s policy, authorities said.

The Oakland Police Department’s Homicide Section, OPD Internal Affairs Bureau, the Oakland City Police Commission, the Community Police Review Agency (CPRA), and the Alameda County District Attorney’s Office will all be looking into what transpired when the officers tried to detain Martin.

Oakland Raiders running back Doug Martin (28) runs for a touchdown during the NFL football game between the Denver Broncos and the Oakland Raiders at the Oakland Alameda Coliseum in Oakland, CA (Chris Brown/CSM/Shutterstock)

Martin was born in Oakland and grew up in Stockton. After graduating from high school, he attended Boise State, where he became one of the “best running backs in school history,” according to the university.

Martin became the first Boise State running back to be selected in the first round of the NFL Draft and one of six overall, according to the university. He was later drafted by the Tampa Bay Buccaneers with the 31st pick of the 2012 Draft.

“He just had this dynamic smile,” former Buccaneers coach Dirk Koetter told AP News. “The guy was always smiling. He was a great teammate, always upbeat in the building. Everyone enjoyed being around him.”

Martin described his running style as aggressive and relentless. During his career with Tampa Bay, he twice ran for more than 1,400 yards, but he failed to come close to that in the other four years mainly because he was hurt.

He spent his final year in the NFL with the Oakland Raiders.

“Doug Martin’s distinguished NFL career — including two Pro Bowl appearances and a 2015 All-Pro honor — was celebrated by countless fans,” Murphy said. “Off the field, Doug was deeply committed to serving the communities of Boise, Idaho, Stockton, and Oakland, California, where his generosity and spirit were well known.”

AP News contributed to this report.