(CNN) Hannah Williams' father still has no idea why a police officer shot and killed his 17-year-old daughter.

"We just need to know what happened that night because they haven't told us anything, nothing. Everything I've learned is from media or on Twitter, like everything. No one come to talk to us," Hannah's sister, Nyla, 19, told reporters Thursday.

It's been almost a week since the California teen encountered a Fullerton police officer while driving in the nearby city of Anaheim.

At some point, Hannah's car and the officer's police SUV "made physical contact," the Orange County District Attorney's office said.

"An officer-involved shooting occurred and a replica Beretta 92 FS handgun was recovered at the scene next to" the teen, the prosecutor's office said. "The gun was later identified as a replica handgun designed to look like a real Beretta 92 FS."

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