The coffin is not still shut. The team has lifted the lid.
Known. It was found with the lime mortar on its stone lid still whole.
The coffin was found on Zorina Street in Cavtat, the ancient Roman town of Epidaurum, in Croatia. It lay about three metres down. It weighs about five tons. It is a Salona type, linked to workshops in Salona. Experts date it to between the 4th and 6th centuries AD. It had stayed sealed for more than 1,500 years. Inside were the remains of one person. The bones were fragile and poorly kept. Organic material from the coffin, and pieces of the mortar seal, are going to a laboratory.
The page does not say what is still argued.
https://www.ancient-origins.net/news-history-archaeology/sealed-roman-sarcophagus-00102891