"There's a strong possibility that the two homicides we had are connected, but we can't say definitively yet," French said.
She said it is also likely that the murders in Richmond were connected to one in unincorporated North Richmond, but as of Tuesday morning, no suspects had been identified or arrested in any of the cases.
The first shooting was reported in Richmond at about 8:30 p.m. near the intersection of Ohio Avenue and South 39th Street.
When officers arrived, they found a man suffering from gunshot wounds. He was taken to a hospital and is expected to survive, French said.
The second shooting happened shortly before 10:30 p.m. in the 100 block of West Ruby Avenue in unincorporated North Richmond, sheriff's spokesman Jimmy Lee said.
Deputies found two gunshot victims in front of a home. One victim, 28-year-old North Richmond resident Ray Anthony Hutson Jr., died at the scene, Lee said.
The second victim was critically injured and was taken by helicopter to John Muir Medical Center in Walnut Creek. Lee said this morning that his condition has since been upgraded to serious.
The next shooting was reported shortly after 11 p.m. in the 3200 block of Center Avenue in Richmond.
The victim in that case, identified by the Contra Costa County coroner's office as 19-year-old Richmond resident Rashad Bailey, was shot and killed while sitting in his car.
French said Bailey had been visiting friends and was preparing to leave when he was killed.
About 15 minutes later, another shooting was reported near the intersection of Macdonald Avenue and First Street.
In that shooting, Darrell Duncan Jr., a 26-year-old Richmond resident, was killed and another man was injured but is expected to survive, French said.
No suspect descriptions were available this morning for any of the shootings.
French said Richmond police detectives are working with sheriff's investigators on the cases, and that the Police Department has been assigning additional officers to certain areas in an effort to prevent retaliation.
The two deaths in Richmond brought the city's total number of homicides so far this year to 14, French said.