Turkish security sources revealed that cellphones message chats of a suspect arrested in connection with last Sunday’s terrorist bomb attack in Istanbul are turning up evidence of the deadly attack.

After last week’s deadly attack in the heart of Istanbul, the Police Anti-Terrorism Division examined the phone of Ammar J., the brother of confessed bomber Ahlam Albashir, said the sources, who asked not to be named due to restrictions on speaking to the media

In a WhatsApp message, Ammar J., who was arrested as part of the inquiry, told his sister after the explosion, which killed six people and injured 81, to “take off the clothes and put them in a bag.”

Ammar J. also reportedly emailed an image of Albashir to a person named Halil M. with the words, “This is her,” to which Halil M. replied, “Notify me.”

According to security sources, Ammar J’s phone calls are considered evidence that he was aware of the explosion in advance and assisted the terrorist.

Ahlam Albashir confessed to the bombing soon after the attack, and dozens of suspects in the terrorist act have either been detained or arrested.