See the references in the documentation:
Chalmers, R. P. & Flora, D. B. (2015). faoutlier: An R Package for Detecting Influential Cases in Exploratory and Confirmatory Factor Analysis. Applied Psychological Measurement, 39, 573-574. doi: 10.1177/0146621615597894
Flora, D. B., LaBrish, C. & Chalmers, R. P. (2012). Old and new ideas for data screening and assumption testing for exploratory and confirmatory factor analysis. Frontiers in Psychology, 3, 1-21. doi: 10.3389/fpsyg.2012.00055
For the forward search, see:
D. Mavridis and I. Moustaki, “Detecting Outliers in Factor Analysis Using the Forward Search Algorithm,” Multivariate Behavioral Research, vol. 43, pp. 453–475, 2008, doi: 10.1080/00273170802285909.