OAKLAND, Calif. (AP) — Prosecutors on Wednesday added charges that could qualify a man for the death penalty if he's convicted of stabbing 18-year-old Nia Wilson to death at a train station in Northern California.

Alameda County prosecutors added the special-circumstances enhancement of "lying in wait" to the charges against John Cowell, who didn't enter a plea during a court hearing, the East Bay Times reported .

Cowell, 27, is charged with murder in the fatal stabbing of Wilson last month as she changed trains at a subway station in Oakland as well as attempted murder in the attack that also wounded Wilson's sister.

Alameda County District Attorney Nancy O'Malley said authorities are still investigating whether Cowell was motivated by racial hate in the attack. The women are black, and he is white.

O'Malley said last month after Cowell appeared in court for the first time that there hasn't been any evidence of a hate crime but that such a charge could be filed if investigators find any proof of that as a motive.

Alameda County Public Defender Brendon Woods, who is Cowell's attorney, said he doesn't agree with the added special-circumstance allegations and that there is no evidence the crime was fueled by racism.

"I'm deeply concerned that they're now seeking death, possibly for someone that has severe, severe mental illness," Woods said.

"What we have here is someone who was released by a state hospital just 75 days before this incident," Woods added. "He suffers from severe mental illness, and that's why we're here today."

Whether or not prosecutors decide to seek the death penalty will occur after a hearing in which a judge will determine if Cowell should be held on his charges. A date for that hearing has not yet been set.

California hasn't executed anyone since 2006 and has the nation's largest death row with nearly 750 inmates.