Dennis Jackson entered a conditional guilty plea to a seven-count indictment charging him with assault, drug, and firearm offenses. He was sentenced to a total of 271 months imprisonment and 5 years supervised release. On appeal, Jackson challenges the district court’s 1 denial of his motion to suppress evidence seized pursuant to a warrant, arguing (1) there existed insufficient probable cause, (2) the federal agents failed to knock and announce their intentions properly as required by 18 U.S.C. § 3109, and (3) the federal agents obtained a warrant to search for firearms as a pretext to search for drugs. For the reasons that follow, we affirm.

Reviewing for clear error the district court’s factual findings and de novo its legal conclusions based on those facts, we find that a substantial basis existed for concluding that the search would uncover evidence of wrongdoing, given the existence of specific incriminating information furnished by a cooperating individual who had proven reliable in the past, along with corroborating evidence. See United States v. Allen, 297 F.3d 790, 794 (8th Cir. 2002) (standard of review; judicial determination of probable cause will be upheld if there was substantial basis for concluding that search would uncover evidence of "wrongdoing); United States v. Goodson, 165 F.3d 610, 614 (8th Cir. 1999) (statements of reliable confidential informant are themselves sufficient to support probable cause for search warrant; reliability of informant can be established if person has history of providing law enforcement officials with truthful information).

We also agree with the district court that the federal officers, who attempted to telephone Jackson and repeatedly knocked and yelled, “Police, search warrant,” before breaking open the door, did not violate section 3109. See 18 U.S.C. § 3109; United States v. Lucht, 18 F.3d 541, 548-49 (8th Cir. 1994) (standard of review; upholding finding that § 3109 was not violated where officers had been constructively refused admittance by occupants’ silence for 20 seconds after officers knocked and announced their presence and purpose). Finally, the officers’ expectation that they would find drugs while searching *766 for unlawful firearms did not undermine the validity of the warrant to search for firearms. See United States v. LaMorie, 100 F.3d 547, 552 (8th Cir. 1996).

Accordingly, we affirm.