Wasn't pleased with the fact you couldn't retrieve the BTC so was looking into it again. (No need for a 2nd reward though.)
Is there a possibility you tried a "BTC doubler" or HYIP scheme by that time?
The address: 37zfKL5EqsokYztEj6yrJxeJah52CgJixG is connected to a forum user:
https://bitcointalk.org/index.php?action=profile%3Bu%3D778507This user / wallet is connected to some ponzi schemes.
Source.
(don't know how i could oversee this yesterday)
Probable websites (not advisable to visit them, i haven't checked for malicious activities!):
http://Bitcoincopy.site123.me
http://Multiplybitcoin.com
http://Btc48hours.com
http://mmmglobal.org/?i=lex
I can't find any related websites to the other wallets though.
According to bitcoinwhoswho, the address received its latest transaction in 2017, so it has stopped receiving BTC. This might be due to the 'owner' shutting the sites down.
Says the wallet is connected with 4 possible Hyip scams, so it's been used for illegal activity.
Not only that, I checked the transaction link you added, and it said that your friend sent the btc to the address, this might imply that he sent them to a HYIP owner.
Unfortunately, there is simply no way for bittrex to get the BTCs back, not only because the btc transaction is basically irreversible, but also because the transaction is old enough, he sent them in 2017.
Here's my address: 373dAiDkUX6cfkadmWcbeJHbHhxpZScDP6