Singh is accused of causing a fatal crash in Selma.
The crash killed 8-year-old Maverick Martzen and inflicted serious injuries on Maverick's parents - Scott and Megan Martzen.
Singh was arrested Wednesday night after being released into ICE custody Tuesday.
Singh also faces a charge for driving on a suspended license because of a prior DUI.
NEW: The Fresno County DA’s office has filed a murder charge against Karmjit Singh, the driver arrested for DUI after Saturday night’s crash that killed an 8-year-old boy.@ABC30 pic.twitter.com/GuT8mgZDOX— Corin Hoggard (@corinhoggard) February 28, 2019
Of note: They did*not* charge him with DUI, but Singh was on probation for a 2016 DUI in Tulare County and was not allowed to drive.— Corin Hoggard (@corinhoggard) February 28, 2019
This is a developing story. Below you'll find an earlier report.
The baseball bat left among the flowers at the scene of a deadly crash has a special meaning for the family hit by an alleged drunk driver.
RELATED: 8-year-old boy killed in DUI crash on what neighbors call deadly Selma cross streets
"Maverick was a very active little boy who loved baseball, playing baseball," said Jeff Hammerschmidt.
8-year-old Maverick Martzen died when a BMW blew through a stop sign and T-boned his family's car Saturday night. CHP officers say witnesses estimated the car's speed at about 100 miles per hour and they believe 35-year-old Karmjit Singh was drunk at the time.
But they say Singh told them he couldn't take a breathalyzer and by a Tuesday deadline for prosecutors to file charges, investigators still hadn't gotten proof he was drunk.
The district attorney's office decided that meant they shouldn't file any charges yet, even though they could've filed a simple manslaughter case.
RELATED: ICE issues immigration detainer on driver in deadly Selma DUI crash
"The problem with that is if the case would get to arraignment which would be this week and the defendant pled to those charges, that would forever bar the vehicular manslaughter under the influence of alcohol or the murder under the influence of alcohol," said Hammerschmidt.
Action News found court records showing Singh has a prior DUI conviction from Tulare County in 2016.
If testing reveals he was under the influence this weekend, he would face 15 years to life, plus six more years for inflicting serious injuries on Maverick's parents - Scott and Megan Martzen.
Hammerschmidt defended Megan Martzen in a high profile criminal case in 2010, and he visited the family this week in the hospital.
He says they may have months of physical rehabilitation ahead of them, and the emotional hole in their family is irreparable.
"One of the things I think is helping them is how close they are as a family," he said. "They're all supporting each other, and you can feel that in the room. Obviously, they're going through a really difficult period, but I think they're handling it as well as can be expected."
The video above is from an earlier broadcast and will be updated.