The search for missing Centers for Disease Control and Prevention (CDC) employee Timothy Cunningham entered its third week with no clue as to the whereabouts of the 35-year-old, who disappeared after leaving work because he felt sick. On Monday, police said they found no evidence of foul play in the mysterious disappearance of Cunningham.

Cunningham was last seen at work on Feb. 12, the Atlanta Police Department said, adding they have received multiple tips and are investigating the case. Cunningham's parents' agony increase as in four instances police told them about a body being found, only to later find that it was not that of their son's.

"It takes you to a place that the light is not shining in," his father Terrell Cunningham said. "I won't call it a dark place, but they are lows. This is extremely hard."

Cunningham's parents drove down from Maryland after they hadn't heard from their son. According to local reports, the parents found Cunningham's phone, keys, wallet, car and dog at his house.

"Everything about this disappearance is unusual," his father said. His mother added, "We really need him back to complete our circle."

The parents said they feared something was wrong with their son on the evening of Feb. 11, after they spoke with him over the phone and exchanged a series of text messages.

“We’ve shared that with the detectives, and we’ve kept that as a private matter,” his father said. “As a parent, you have indicators when things are just not right with your child, and that was the case.”

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His mother said she received a text message early morning of Feb. 12. that read: “Are you awake?” The mother said she saw the message later as her phone was on silent mode.

“I wish I had that opportunity to answer that text,” she said.

Cunningham, a commander with the United States Public Health Service, who has responded to Superstorm Sandy along with the Zika and Ebola outbreaks, worked at the agency’s Atlanta headquarter. According to Cunningham's CDC bio, he is currently a team lead with the CDC’s Division of Population Health and trained with the CDC as an Epidemic Intelligence Service officer.

The CDC in a statement called Cunningham "a highly respected member of our CDC family."

"Dr. Cunningham's colleagues and friends at CDC hope that he is safe," the statement said. "We want him to return to his loved ones and his work -- doing what he does best as a CDC disease detective -- protecting people's health."

Cunningham's family has partnered with Crime Stoppers of Greater Atlanta to offer a $10,000 reward for information in the case.

"My first mind is that something has happened especially considering the length of time he's been gone. Not having his phone, leaving his dog Bo alone, he just wouldn't voluntarily check out like that," his brother, Anterio Cunningham, told Fox5 on Monday.

CDC Atlanta
A general view of the Centers for Disease Control and Prevention headquarters in Atlanta, Sept. 30, 2014. Reuters/Tami Chappell