Updated at 4:25 a.m. Feb. 7, 2013

Carrying two toddlers in his arms, a San Diego man rang the intercom button Wednesday at the Imperial Beach sheriff's substation to report a murder. He had just killed his wife, he reportedly said.

Homicide Lt. Glenn Giannantonio said Marvin Duncan, 59, rang the substation's button around 3:40 p.m. to inform deputies of the crime. "The deputy detained the man and the children were taken into protective custody," Giannantonio said.

The children were not injured, he said. Deputies went outside to find Rocio Duncan, 36, suffering from multiple stab wounds outside a Nissan Titan truck.

"The woman was still breathing but succumbed to her injuries shortly after she was discovered," he said.

Marvin Dennis Duncan was booked into County Jail at 3:07 a.m., according to jail records, and was being held on first-degree murder charges with no bail. He is to be arraigned at 1:30 p.m. Friday at South County Superior Court in Chula Vista.

The Sheriff's Department shares the parking lot in the 800 block of Imperial Beach Boulevard with City Hall, the Imperial Beach Public Safety Department and Imperial Beach Fire Department. Imperial Beach Boulevard between Delaware and 9th streets were closed off Wednesday, and City Hall and the sheriff's substation were surrounded with "Sheriff's Line Do Not Cross" tape during the investigation.