HONOLULU -- Japanese visitor Masumi Watanabe has been missing since last April, and Monday a pest-control technician went on trial for her death.

Prosecutors said their biggest challenge is to prove the murder without knowing the cause of death, without a weapon and without an eyewitness.

They said a store photo of the Kirk Lankford buying a shovel the night Watanabe disappeared helps a lot.

That picture came from Home Depot and was taken just before 10 p.m. and also showed Lankford in his work uniform buying gloves, duct tape and trash bags -- 12 hours after Watanabe went during her daily walk in Pupukea. Prosecutors also showed pictures of blood from Lankford's truck.

"Her blood was on the passenger floor mat, her blood was on the passenger floor panel her blood was on the passenger seat," said Peter Carlisle, the Honolulu prosecutor.

He said the blood matched Watanabe's DNA.

One witness, Stephen Paty, said he saw Watanabe gesturing to someone in a light-colored pick-up on Pupukea Road.

"To me, it was an obvious wave off, she was saying no to something," said Paty. "Whatever it was they were talking about, she was saying no."

Lisa Nakayama, another witness, said she saw Watanabe get into a Hauoli Pest Control truck, and later learned she was missing from TV.

"My heart started pounding and my hands started shaking because I recognized her," said Nakayama.

The prosecutor used GPS records from the Hauoli truck, along with store surveillance and purchase records to show that Lankford had ample time between appointments to hide a body and buy clean-up materials.

Later, after the Home Depot surveillance photo was taken, Lankford was seen using the shovel at Kahana Bay. A man used his knife and road markings to record his license-plate number.

Lankford's attorney is keeping his strategy secret, but many speculate that Lankford will claim that he accidentally killed Watanabe and panicked. Although when questioned by police, he denied he'd ever seen her.

The trial will last into next week.