For over 200 years, they did not know who rested in the sarcophagus. The archaeologist has the answer

Archaeologist Warwick Rodwell claims to have solved the mystery of a Roman sarcophagus discovered over 200 years ago at Westminster Abbey. Although the stone coffin dates back to the 4th century, the remains inside are believed to belong to a medieval abbot from the 11th century. The sarcophagus was first found in 1820, with excavations occurring in 1869. Rodwell suggests it was moved from its original burial site and may have belonged to a wealthy Roman named Valerius Amandinus. The presence of a later-added cross indicates it was reused for burial. Radiocarbon dating shows the remains are from the late 10th or early 11th century, likely belonging to either Ælfwig or Wulfnoth, both abbots of Westminster. Rodwell posits that Ælfwig is the more probable candidate due to his tenure as abbot.