On Thursday afternoon, the Tulare County District Attorney's Office charged the 52-year-old with Alexander's murder, one day after his arrest during a traffic stop in Porterville.
Authorities say surveillance video shows Watson offering Alexander a ride.
Her family also received a number of tips in the case.
"They assured my family that they were going to work fast and catch the person that killed Dynasty," said Carlton Jones, Alexander's cousin. "And 48 hours later they caught him and today I got to watch him be arraigned."
Carlton Jones says he came to the arraignment to show support for his cousin, while her mother prepares funeral arrangements.
Also on Thursday, the Tulare County Sheriff's Office released Alexander's autopsy results, which showed she died of a single gunshot wound to the upper body.
Her body, which was found near an orchard just south of Tulare, also showed signs of strangulation.
"(It's) not really reassuring when he was obviously a criminal and he was just out walking around freely, driving until he killed someone," Jones said. "So hopefully my little cousin didn't die in vain and this person will never be out on the streets ever again."
A memorandum filed Wednesday by the Tulare County Probation Department provides a closer look at Watson's recent criminal history.
He had several arrest warrants for failing to appear in court and violating probation.
In a 2016 misdemeanor assault and battery case, two different judges ordered Watson to go to an anger management program, but he never went.
Watson is being held without bail.
He'll be back in court a week from Thursday.