Authorities released the identity Tuesday of a man who plunged into the bay and was found dead in the water after he allegedly fled deputies in a truck and rammed a gate at Oakland International Airport.

Aptos resident Bryan Hirano, 42, entered the water Sunday after fleeing from deputies in his truck following a stop sign violation, according to the Alameda County Sheriff’s Office.

Authorities do not know what motivated Hirano to risk his life following a minor traffic offense, said Sgt. Ray Kelly, a sheriff’s spokesman. Authorities found an “arsenal” of airsoft pellet guns, which resemble real firearms, in his truck. Officials also found masks, hoods and binoculars.

Personnel from the U.S. Coast Guard’s San Francisco sector discovered Hirano’s body at 11:16 a.m. Monday after receiving a report of a body floating in the Oakland Estuary, said Coast Guard Lt. Athena Stricker. The body was processed by the Alameda County coroner’s office.

Authorities found Hirano’s body about 4 miles from where he plunged into the water. The location “would be consistent with the tides and the movement,” Kelly said.

Officials determined the man is the registered owner of a Chevrolet truck from Santa Cruz County that sheriff’s deputies were chasing for a stop sign violation.

Hirano allegedly drove down an access road used by airport personnel, crashed through a closed gate, then drove about 2 miles along the perimeter of the runway. He then ditched the vehicle and jumped into the water across from Bay Farm Island, officials said.

“He probably stripped off his clothes and tried the swim,” Kelly said. “But the water is 61 degrees in summer, and unless you’re a trained athlete, you’re not going to get very far.”

Operations at the airport were normal, a spokeswoman said Tuesday morning. A Transportation Security Administration spokeswoman said the agency was not involved with the investigation.

Pete Grieve is a San Francisco Chronicle staff writer. Email: pete.grieve@sfchronicle.com Twitter: @pete_grieve