  During its four years of photometric observations, the Kepler space telescope
detected thousands of exoplanets and exoplanet candidates. One of Kepler's
greatest heritages has been the confirmation and characterization of hundreds
of multi-planet systems via Transit Timing Variations (TTVs). However, there
are many interesting candidate systems displaying TTVs on such long time scales
that the existing Kepler observations are of insufficient length to confirm and
characterize them by means of this technique. To continue with Kepler's unique
work we have organized the "Kepler Object of Interest Network" (KOINet). The
goals of KOINet are, among others, to complete the TTV curves of systems where
Kepler did not cover the interaction timescales well. KOINet has been
operational since March, 2014. Here we show some promising first results
obtained from analyzing seven primary transits of KOI-0410.01, KOI-0525.01,
KOI-0760.01, and KOI-0902.01 in addition to Kepler data, acquired during the
first and second observing seasons of KOINet. While carefully choosing the
targets we set demanding constraints about timing precision (at least 1 minute)
and photometric precision (as good as 1 part per thousand) that were achieved
by means of our observing strategies and data analysis techniques. For
KOI-0410.01, new transit data revealed a turn-over of its TTVs. We carried out
an in-depth study of the system, that is identified in the NASA's Data
Validation Report as false positive. Among others, we investigated a
gravitationally-bound hierarchical triple star system, and a planet-star
system. While the simultaneous transit fitting of ground and space-based data
allowed for a planet solution, we could not fully reject the three-star
scenario. New data, already scheduled in the upcoming 2018 observing season,
will set tighter constraints on the nature of the system.
