01/29/2014 01:42 pm ET Updated Jan 29, 2014

Avonte Oquendo Left School Through Open Door, New Surveillance Video Shows

Newly obtained surveillance footage shows Avonte Oquendo walking through a school door left open for more than 30 minutes, NY1 reports. The autistic New York City teen went missing for over three months before his remains were discovered last week.

In the video, an unidentified man wearing a red shirt can be seen leaving through the door, but failing to fully close it behind him. Thirty-one minutes later, Avonte runs towards the open door, looks around, and exits onto Center Boulevard School in Long Island City, Queens.

Shortly after, a school safety agent approaches and closes the door.

"The broadest way of speaking about it is never again," said the family's attorney's, David Perecman, in response to the video."Don't let children leave school between bringing them to school and getting them home. They can't disappear."

The disappearance of Avonte, who was last seen on October 4, sparked a massive city-wide search to find the severely autistic teenager. On January 21, a DNA test confirmed human remains discovered on a Queens beach to belong to Avonte.

At his funeral last Saturday, family and strangers who volunteered to help track down Avonte gathered to pay their respects.

In December, Perecman pointed to an internal investigation conducted by the Department of Education as evidence that school administrators committed serious errors and were delayed in responding to Avonte's disappearance.

Avonte's mother, Vanessa Fontaine, has filed a claim against the NYPD to overturn the "city's denial of her request for the investigative documents" surrounding her son's disappearance, CNN reported last week.