Omar Mateen killed 49 people at Orlando's Pulse nightclub in June 2016.
The Florida gunman had pledged allegiance to the militant group before he killed 49 Orlando clubgoers.
President urges Congress to pass legislation to restrict access to semi-automatic weapons.
A local broadcaster said the message was posted in the men-seeking-men section of Craigslist in San Diego.
After the worst mass shooting in U.S history, McConnell said he was open to suggestions from experts on legislation that could address the problem.
She could soon be charged in connection with the deadliest mass shooting in modern U.S. history.