Douglas

Douglas was a British citizen, who lived and worked in London in the mid-nineteenth century.

Douglas worked as a butler for Lady Ursula, a rich, old woman living in Westminster. When Lady Ursula's health started failing her, she made up her will, leaving her best china to Douglas and his bethrothed, Miriam, and all her other worldly possessions to her cat Mittens.

When Mittens died because of an accident involving a milk wagon, Lady Ursula started visiting Thaddeus the Great, hoping to communicate with her deceased cat and learn to whom she should now leave her fortune. Douglas accompanied her to the séances, bribing the spiritualist into telling Lady Ursula to leave him the money.

However, Anne Roberts discovered that Thaddeus was in the habit of revealing his swindle before moving on to the next city, and warned Douglas about this. Since he was present at every séance, she urged Douglas to take care of the matter. During the final séance, when the lights went out, Douglas made use of the opportunity to stab Thaddeus in his neck, killing him immediately.

Jacob or Evie Frye investigated the murder, interrogating Douglas and all of Thaddeus' clients. When he was eventually confronted with the evidence of his crime, Douglas confessed to the murder, after which he was taken away by the Metropolitan Police Service.

Reference

 * Assassin's Creed: Syndicate - The Dreadful Crimes