When Olson was reported missing on Thursday, police were told that the 6-year-old was taken by another individual. However, the last time he was seen by anyone outside his family was on April 30, the last day he attended school, according to Houston police.

“It’s cause for concern,” Kese Smith, a public information officer for the Houston Police Department, told Newsweek when asked about the lapse in time from when he was last seen at school and the last time family members say they saw him.

On Monday, Houston Police Department Executive Assistant Larry Satterwhite said they have many reports about where he was and why and police are trying to “verify all of that information.” A “complicated case,” Satterwhite added that law enforcement is trying to “move with as much urgency as we can.”

Given that the last time anyone aside from the people who are closest to him saw Olson was on April 30, Satterwhite said it’s possible he’s been missing for weeks. Another possibility police are looking into is whether Olson’s mom was the last person to see him. Theresa Balboa, Olson’s father’s girlfriend, told KTRK she saw the 6-year-old on Thursday.

“I was going to take Sam to school when his mother showed up with the police officer, or who I was under the impression to be a police officer, and they demanded me to release Sam,” Balboa told KTRK.

When asked about this account of the child’s whereabouts, Satterwhite said they have not been able to verify that information and they’ve talked to “all parties involved.” Olson’s biological father and mother have joint custody, according to court records. All have denied having the child.

On Monday, police searched a residence belonging to someone the father’s girlfriend knew and Satterwhite identified it as a place where the child was known to be kept with someone who was watching him.

“We didn’t know if we had a child custody issue we could still have that or anything else more nefarious. We just don’t know or even if we were getting accurate information,” Satterwhite said. “Everybody’s saying what happened and again we’re just trying to verify and piece it all together.”

Police were hoping to find Olson at the residence on Monday but did not. Additional residences are likely to be searched, according to Satterwhite.

Tim Miller, the founder of Texas EquuSearch, a nonprofit that helps locate missing people by way of a horse-mounted search, told KTRK he didn’t have a “good feeling” about the case. Helping to drive his uneasy feeling is that police can’t find someone credible to tell them the last time he was seen and where.

When asked on Monday how no one knows where a 6-year-old child is, Satterwhite said it was a “good question” that he would find out the answer to.

Anyone who sees Olson is encouraged to call the Houston Police Department Missing Persons division at 832-394-1840.