An Indiana Department of Correction spokesman says the investigation into the escape of three state prison inmates is expected to be wrapped up by the end of the month.

Doug Garrison said the age of the prison played a key role in the escape as the inmates made their way through old utility tunnels that led outside the structure.

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He said officials are investigating whether the inmates may have manipulated guards into allowing them into the tunnels unsupervised. Three guards have been suspended since the escape.

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Garrison declined comment on whether the inmates might have had outside help. However, he said officials are investigating a possible connection between the inmates and a parolee who visited the Michigan City area about the same time as the escape.