Iowa man believes he may have been last person to see missing college student Mollie Tibbetts

An Iowa resident believes he may have been the last person to see Mollie Tibbetts before she disappeared.

Devin Riley says he spotted the 20-year-old University of Iowa student jogging past his home at around 9 p.m. on July 18. She did not show up for work in the small town of Brooklyn the following day.

"I've seen her probably three to four times per week," Riley told ABC News in an interview published early Thursday. "She'd kind of jog down the street and towards the hill. I thought nothing of it until I heard somebody was missing, and it really hit me that I hadn't seen that runner since then."

Riley tells "Good Morning America" that Mollie was "wearing like a neon pink sports bra with black khaki yoga pants and an armband with her music device, or phone ... hair in a ponytail, just jogging like normal, any other day."

He reported the sighting to the Poweshiek County Sheriff's Office and received a visit from investigators.

A woman in Marion, Iowa alerted authorities that she spotted Mollie in a store on Wednesday, but cops determined it was not her after watching surveillance video.

"It was unfounded, but we still appreciate this good Samaritan at least reached out," Tom Daubs of the Marion Police Department told the Des Moines Register. "Heaven forbid that was really her."

Marion is approximately 70 miles from Brooklyn.

The FBI is involved in the search, along with state and local investigators. The Mollie Tibbetts reward fund has grown to more than $300,000, according to Crime Stoppers of Central Iowa.

"It's gut-wrenching to know that I could have my daughter out here, and I could go inside for a minute and she could be gone," Riley told ABC. "You assume when you move to a small town that pretty much everyone is close close-knit, everyone knows everyone ... you just do not expect it to happen in a town like this."