Dear Boss is the last Ripper Letters activity in the Jack the Ripper DLC: Weaversbrook needs to know whether the 'Dear Boss' letter came from a madman or a newspaperman, so Evie follows its suspected author to a dockyard and makes him talk.
Tail the man without losing him, listen in once he stops at the dockyard, then frighten and catch him. After his confession you let him run.
The real 'Dear Boss' letter came first, not last: dated 25 September 1888, it reached the Central News Agency on 27 September and was passed to Scotland Yard two days after. Like the in-game copy, it was signed Jack the Ripper.
Evie first reads the Dear Boss text in Jacob's lodgings in The Unfortunates, noting the papers printed it three days before Stride and Eddowes were killed.
This suspect leads you further than the other two, all the way to a dockyard, before he stops to brag, so expect a longer tail.
This is the last of Weaversbrook's three Ripper Letters. The suspects turn out to be a prankster, a political campaigner and a man trying to stir sympathy for the poor; none of them is the killer.
From Hell
From Hell is the first Ripper Letters activity in the Jack the Ripper DLC: handwriting experts have named a suspect for a new letter, and Arthur Weaversbrook asks Evie to make sure he is not the real killer.
Jack's Lieutenants: City of London
Jack's Lieutenants: City of London is an assassination activity in the Jack the Ripper DLC: four of Jack's gang bosses meet at Cannon Street station, and Evie infiltrates the station to kill them all for Arthur Weaversbrook.
Saucy Jack
Saucy Jack is the second Ripper Letters activity in the Jack the Ripper DLC, named after the real 'Saucy Jacky' postcard. Evie runs down its supposed author for Arthur Weaversbrook and finds a man with a political motive.
Letters of Intent
Letters of Intent is the fifth Jack the Ripper memory, dated 3 November 1888: Evie gets a lead from Abberline, rescues newspaper owner Arthur Weaversbrook from Rooks near St Paul's, and then frees his kidnapped son from Jack's men at the docks.