BOSTON (CBS) – Police are investigating reports of another sexual assault on the Esplanade that occurred early Sunday morning.

A man told a Boston University Police officer just before 3 a.m. that he believed a woman had been sexually assaulted on the Esplanade earlier in the night. That man said he came across the 20-year-old local college student, who told him that she had been assaulted and thrown into the Charles River.

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By the time officers arrived, the woman had already gone home, but left her purse with the man who initially alerted police. Police then used her information to track her down at her home, where she refused medical attention and did not provide a description of the suspect.

Police are still investigating four sexual assaults in recent years, three of which that occurred on the Esplanade and one that occurred in South Boston, that are connected. The suspect in each of those cases was described as a clean-shaven African-American male in his mid-20’s to mid-30’s and standing 5’8″ – 5’10” tall. At the time of those assaults, he had a medium-to-large build and was bald.

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Read: Esplanade Assault In April

Officials with the Mass. State police, Boston police and the Suffolk County district attorney’s office are all investigating. They have not determined whether Sunday morning’s incident is linked to the previous sexual assaults.

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Anyone traveling along the Esplanade at night is urged to be vigilant and call 911 if they feel they are in any danger.