In 1999, authors Allen Weinstein and Alexander Vassiliev learned that Soviet files indicate that Dickstein was a paid agent of the NKVD.

This led him to investigate independently the activities of Nazi and other fascist groups in the U.S.[7][8] In 1932, Dickstein joined forces with Martin Dies Jr. to outlaw membership in the Communist Party of the USA.

[8] In 1933, he called for congressional investigation into Anarchism, following the failed assassination attempt of U.S. President Franklin Delano Roosevelt by Giuseppe Zangara.

[11][7] One of the first investigations by the Special Committee was the "Business Plot", an alleged 1933 political conspiracy, which, according to retired Marine Corps Major General Smedley Butler, wealthy businessmen were plotting to create a fascist veterans' organization with Butler as its leader and stage a coup d'état to overthrow President Franklin D. Roosevelt.

Nonetheless, the Special Committee "delet[ed] extensive excerpts relating to Wall Street financiers including Guaranty Trust director Grayson Murphy, J. P. Morgan, the Du Pont interests, Remington Arms, and others allegedly involved in the plot attempt.

Following the 1938 German takeover of Austria, Dickstein attempted to introduce legislation that would allow unused refugee quotas to be allocated to those fleeing Hitler.

They were unaware of his spying or his bribery, but they did know he brutally browbeat and threatened witnesses, grossly exaggerating evidence, and they removed him from membership on the committee.

Moscow concluded that Dickstein was "heading a criminal gang that was involved in shady businesses, selling passports, illegal smuggling of people, [and] getting citizenship.

"[3] In his 2000 book The Haunted Wood, writer Allen Weinstein wrote that documents discovered in the 1990s in Moscow archives showed Dickstein was paid $1,250 a month from 1937 to early 1940 by the NKVD (equivalent to $26,500 in 2023), the Soviet spy agency, which hoped to get secret Congressional information on anti-Communist and pro-fascist forces as well as supporters of Leon Trotsky.

Dickstein also unsuccessfully attempted to expedite the deportation of Soviet defector Walter Krivitsky, while the Dies Committee kept him in the country.

[10] Duffy stated: Dickstein denounced the Dies Committee at NKVD request ("a Red-baiting excursion") and gave speeches in Congress on Moscow-dictated themes.

[3] The Boston Globe stated: "Dickstein ran a lucrative trade in illegal visas for Soviet operatives before brashly offering to spy for the NKVD, the KGB's precursor, in return for cash.

"[8] Joe Persico wrote, "The files document Soviet spying by Representative Samuel Dickstein of New York, so greedy that his handlers gave him the code name Crook.