The on-scene portion of the investigation into what caused the KTVK and KNXV news helicopters to collide in mid-air on Friday is expected to wrap up some time today, with the preliminary report expected by Friday.

The investigators from the National Transportation Safety Board drained the pond at Steele Indian School Park.

They were searching for debris from Friday's crash, which took the lives four Valley journalists, including two from 3TV.

The investigators now have the tough job of taking the pieces of the destroyed helicopters and putting them together to help them understand what happened.

"We're going to replace all the pieces that we can identify in the locations that we know where they came from on the airplanes and try to determine from that those pieces what actually happened," explained NTSB spokesman Steve Chealander. "In other words, we are going to look at strike marks and all kinds of data from those pieces to determine what happened."

The NTSB said it could take up to nine months to release its final report.

Investigators said some of the most important information they will get as they look into the incident will come from witnesses.

To that end, they've established a witness hotline. That phone number is 602-262-6141.

In the meantime, the memorial at the entrance to the park continues to grow as people from all over the city pay their respects to those killed in the accident.

The general public is invited to view the memorial services of Mr. Jim Cox and Mr. Scott Bowerbank live in the main worship center at North Phoenix Baptist Church, 5757 N. Central Avenue in Phoenix, Arizona. The church is located on the southeast corner of Central Avenue and Bethany Home Road. The services begin at 11 a.m. and will also be broadcast live on Channel 3 and streamed on azfamily.com.

Services for Channel 15 pilot Craig Smith will be 10 a.m. Thursday, at La Casa de Cristo Lutheran Church in Scottsdale.

And a memorial for Channel 15 photographer Rick Krolak, killed alongside Smith, will be 10 a.m. Saturday, at First United Methodist Church in Phoenix.