2 email headers, with different IP addresses, can you determine if the emails came from same computer?

I have 2 email headers, from different senders and different IP addresses. I suspect it is the same person. Is there any way to determine if the emails were sent from the same computer? Can you do this by examining the headers? Both emails were from hotmail accounts to hotmail accounts so the only information I can find in the headers is the IP address. Does anyone know if there are tools that law enforcement or private investigators use to determine if it is the same computer without going through the ISP? Thanks!