[1] He gained "wealth and infamy from the trade in blood,"[2] and sold thousands of people from the Chesapeake region to parts south.

[3] Slatter, in company with Austin Woolfolk, Bernard M. Campbell, and Joseph S. Donovan has been described as one of the "tycoons of the slave trade" in the Upper South, collectively "responsible for the forced departures of approximately 9,000 captives from Baltimore to New Orleans.

[10] He appears to have been in business by 1828, at which time the sheriff of Crawford County, Georgia reported that he had picked up "a negro GIRL, who says her name is Amelia, and that she formerly belonged to Hull Slatter of Jones county, who sold her to a negro trader, whose name she does not recollect—She is about fitteen or sixteen years of age, and of a small size, low and chunkey.

[12] He may have been based in Virginia for a time, and first come to Baltimore, Maryland about 1830, where he had a home and office on West Ball Street.

[13] A Maine-born Baltimore schoolteacher and abolitionist named Solon Beale described Slatter's early career in a Bangor, Maine newspaper article of 1855, writing:[14] About 1837–8, Hope Hill Slatter, a son of Methodist parents of Georgia, came to Baltimore having borrowed US$4,000 (equivalent to $107,718 in 2023) of his mother, and embarked in the business of buying and selling slaves.

[6] A religious delegation visited his slave jail in 1840, and one visitor reported in 1843: He addressed them somewhat as follows: 'Gentlemen, I suppose this looks strange to you, coming fram the North as you do.

[8]In the 1840s Slatter caught the attention of abolitionist William I. Bowditch, who included three of his advertisements in his 1849 book Slavery and the Constitution.

— Having returned from New Orleans, I will now pay the highest cash prices for all likely negroes that are slaves for life and good titles.

"[18] In 1844 abolitionist William Jay reprinted a newspaper advertisement of Slatter's that instructed potential clients to seek out his agent at Booth's Garden.

[5] In 1848 The Liberator reported that H. H. Slatter had used four men armed with pistols, clubs and Bowie knives to help him quell a crowd surrounding one of his shipments, likely the people who attempted to escape to freedom in the Pearl incident.

[23] According to Carol Wilson's history of the kidnapping of free people of color in the pre-Civil War United States, "By 1839, the [Pennsylvania Abolition Society] was referring to [George] Alberti as the 'well known' kidnapper.

His reputation spread beyond the Philadelphia area to Baltimore; in 1837 The Liberator carried a report on Alberti's activities in that city.